TRS CONNECTOR

A 'TRS connector', also called a 'jack plug' (UK) or 'phone plug' (U.S.), is a common audio connector. It is cylindrical in shape, typically with three contacts, although sometimes with two (a 'TS connector') or four (a 'TRRS connector'). It was invented for use in telephone switchboards in the 19th century and is still widely used, both in its original quarter-inch (6.3 mm) size and in miniaturized versions. The connector's name is an acronym derived from the names of three conducting parts of the plug: 'T'ip, 'R'ing, and 'S'leeve^[1] – hence, 'TRS'.
In the U. K., the terms ''jack plug'' and ''jack socket'' are commonly used for the respectively male and female TRS connectors.^[2]
In the U. S., a female connector is called a jack. The terms ''phone plug'' and ''phone jack'' are commonly used to refer to TRS connectors,^[3] but are also sometimes used colloquially to refer to telephone plugs and the corresponding jacks that connect wired telephones to wall outlets. The similar terms ''phono plug'' and ''phono jack'' normally refer to RCA connectors. To unambiguously refer to the connectors described here, the diameter or other qualifier is often added, e.g. ''1/4-inch phone plug, 3.5 mm phone jack,'' or ''stereo phone plug,'' for the three-contact version.
The initial application for the TRS connector was in telephone equipment, which explains why, to this day, it is often termed a "phone plug," even though its use in telephony applications ended many decades ago.
The connector's association with stereo headphones possibly helped maintain this term.

Contents

Modern connectors

Mono and stereo compatibility

Uses

Misuse

Switch contacts

Tip/ring/sleeve terminology

Usage

Audio

Computer sound

Recording equipment

Aircraft headsets

Configurations and schematic symbols

See also

References

Modern connectors

Modern TS and TRS connectors are available in three standard sizes. The original 1/4" (6.35 mm) version dates from 1878, for use in manual telephone exchanges—making it possibly the oldest electrical connector standard still in use. The 3.5 mm or 'miniature' and 2.5 mm or 'subminiature' sizes were originally designed as two-conductor connectors for earpieces on transistor radios. The 3.5 mm and 2.5 mm sizes are also referred to as 1/8" and 3/32" respectively in the United States, though those dimensions are only approximations. All three sizes are now readily available in two-conductor (mono) and three-conductor (stereo or tip ring sleeve) versions.
Four and five conductor versions of the 3.5 mm plug are used for certain applications. A four conductor version is becoming a de facto standard output connector for compact camcorders, providing stereo sound plus a video signal. This interface is also seen on some laptop computers. Proprietary interfaces using both four and five conductor versions exist, such as the audio connector on the first four generations of iPod MP3 players (the 5th generation player now uses a standard 3 conductor cable), where the extra conductors were used to supply power for accessories. There is also an optical connector used for TOSLINK (mainly on things like portable equipment; hi-fi separates and similar tend to use the standard square connector) that is the same size as a 3.5 mm jack. Sockets exist that can make either an optical connection to such a plug or an electrical connection to a stereo jack plug.
A three or four conductor version of the 2.5 mm plug is widely used on cell phone handsfree headsets, providing mono (three conductor) or stereo (four conductor) sound and a microphone input. It should be noted that the use of common stereo headphones with the 2.5 mm plug are often not compatible with this type of socket.
Relatively uncommon 'tiny telephone' ('TT') connectors use mid-size phone plugs with a 4.4 mm (0.173-inch) diameter shaft. Due to their compactness and reliability, TTs are often used for professional console and outboard patchbays in studios and live sound applications, in which a single patch panel may require hundreds of patch points in a limited space. The TRS versions of TT connectors are capable of handling balanced line signals and are preferred in pro audio installations
Both two-conductor and three-conductor versions of the three standard sizes are readily available in male (plug) and female (socket or simply "jack") line versions, and panel-mounting female versions. Panel-mounting male versions of these also exist but are rare, as they are vulnerable to mechanical damage and therefore unreliable. Female line versions are also notoriously unreliable and are avoided by many users.
The most common arrangement remains to have the male plug on the cable, and the female socket mounted in a piece of equipment, which was the original intention of the design. A considerable variety of line plugs and panel sockets is available, including plugs suiting various cable sizes, right angle plugs, and both plugs and sockets in a variety of price ranges and with current capacities up to about 15 amperes for the 1/4" version.
Non-standard sizes, both diameters and lengths, are also available from some manufacturers, and are used when it is desired to restrict the availability of matching connectors.

Several obsolete versions of the 1/4" jack plug exist, including:

★ A two-pin version, consisting of two mono 6.3 mm jack plugs at a centre spacing of 1". The socket versions of these can be used with normal jack plugs provided the plug bodies are not too large, but the plug version will only mate with two jack sockets at 1" centre spacing, or with line sockets, again with sufficiently small bodies. These connectors were commonly used on early stereo tape recorders. A similar type of 3.5 mm connector is often used in the armrests of aircraft, as part of the on-board entertainment system. Plugging a stereo plug into one of the two mono jacks typically results in the audio coming into only one ear. Adaptors are available.

★ A short-barrelled version, once used on high-impedance mono headphones, and in particular those used in World War II aircraft. It is physically possible to use a normal plug in a short socket, but a short plug will neither lock into a normal socket nor complete the tip circuit. These are still manufactured but are now regarded as a non-standard size.

Mono and stereo compatibility

In the original application in manual telephone exchanges, many different configurations of 1/4" jack plug were used, some accommodating five or more conductors, with several tip profiles. Of these many varieties, only the two-conductor version with a rounded tip profile was compatible between different manufacturers, and this was the design that was at first adopted for use with microphones, electric guitars, headphones, loudspeakers, and many other items of audio equipment.
When a three-conductor version of the 1/4" jack was introduced for use with stereo headphones, it was given a sharper tip profile in order to make it possible to manufacture jacks (sockets) that would accept only stereo plugs, to avoid short-circuiting the right channel amplifier. This attempt has long been abandoned, and now the normal convention is that all plugs fit all sockets of the same size, regardless of whether they are mono or stereo. Most 1/4" plugs, mono or stereo, now have the profile of the original stereo plug, although a few rounded mono plugs are also still produced. The profiles of stereo miniature and subminiature plugs have always been identical to the mono plugs of the same size.
The results of this physical compatibility are:

★ If a two-conductor plug of the same size is connected to a three-conductor socket, the result is that the ring (right channel) of the socket is grounded. This property is deliberately used in several applications, see "tip ring sleeve", below. However, grounding one channel may also be dangerous to the equipment if the result is to short circuit the output of the right channel amplifier. In any case, any signal from the right channel is naturally lost.

★ If a three-conductor plug is connected to a two-conductor socket, normally the result is to leave the ring of the plug unconnected (open circuit). In the days of valves ("tubes" in the U.S.) this was also potentially dangerous to equipment but most solid state devices tolerate this condition well. A stereo socket could be wired as a mono socket to ground the ring in this situation, but the more conventional wiring in this case is to leave the ring unconnected, exactly simulating a mono socket.

Uses

Some common uses of jack plugs and their matching sockets are:

★ Headphone and earphone jacks on a wide range of equipment. 1/4 in. plugs are common on standalone equipment, while 3.5 mm plugs are nearly universal for portable audio equipment. 2.5 mm plugs are not as common, but are sometimes used on communication equipment such as two-way radios and mobile phones.

★ Microphone inputs on tape and cassette recorders, sometimes with remote control switching on the ring.

★ Patching points on a wide range of equipment.

★ Personal computer sound cards. Stereo 3.5 mm jacks are used for:

★
★ Line in (stereo)

★
★ Line out (stereo)

★
★ Headphones/loudspeaker out (stereo)

★
★ Microphone input (mono, sometimes with 5v power available on the ring)

★ Electric guitars. Almost all electric guitars use a ¼ in mono jack (socket) as their output connector. Some makes (such as Shergold) use a stereo jack instead for stereo output, but more commonly a second mono jack is provided (as with Rickenbacker).

★ Instrument amplifiers for guitars, basses and similar amplified musical instruments. ¼ in jacks are overwhelmingly the most common connectors for:

★
★ Inputs. A shielded cable with a mono ¼ in jack plug on each end is commonly called a ''guitar cord'' or a ''patching cord'', the first name reflecting this usage, the second the history of the jack plug's development for use in manual telephone exchanges.

★
★ Loudspeaker outputs, especially on low-end equipment. Speakon connectors are generally considered superior and so are usually preferred on higher-end equipment, although it is not uncommon to find both provided for compatibility. Heavy-duty ¼ in loudspeaker jacks are rated at 15 A maximum which limits them to applications involving less than 1800 watts. ¼ in loudspeaker jacks commonly aren't rigged to lock the plug in place and will short out the amplifier's output circuitry if connected or disconnected when the amplifier is live.

★
★ Line outputs.

★
★ Foot switches and effects pedals. Stereo plugs are used for double switches (for example by Fender). There is little compatibility between makers.

★
★ Effects loops, which are normally wired as patch points.

★ Electronic keyboards use jacks for a similar range of uses to guitars and amplifiers, and in addition

★
★ Sustain pedals.

★ Electronic drums use jacks to connect sensor pads to the synthesizer module or MIDI encoder. In this usage, a change in voltage on the wire indicates a drum stroke.

★ Some compact and/or economy model audio mixing desks use stereo jacks for balanced microphone inputs.

★ The majority of professional audio equipment uses mono jacks as the standard unbalanced input or output connector, often providing a ¼ in unbalanced line connector alongside (or in a few cases in the middle of!) and as an alternative to an XLR balanced line connector.

★ Modular synthesizers commonly use monophonic cables for creating patches.

★ ¼ in connectors are widely used to connect external processing devices to mixing consoles' insert points (see Insert (effects processing)). TRS or TS connectors might be used in pairs as separate Send and Return jacks or a single TRS jack might be employed for both Send and Return in which case the signals are unbalanced. The single unbalanced combination Send/Return TRS insert jack saves both panel space and component complexity. Note that mixing console insert points can also be XLR, RCA or Bantam TT (tiny telephone) jacks, depending on the make and model.

★ Some small electronic devices such as audio cassette players, especially in the cheaper price brackets, use a two-conductor 3.5 mm or 2.5 mm jack as a DC power connector.

★ Some photographic studio strobe lights have ¼ in or 3.5 mm jacks for the flash synchronization input. A camera's electrical flash output (PC socket or hot shoe adapter) is cabled to the strobe light's sync input jacks. Some examples: Calumet Travelite, and Speedotron use a ¼ in mono jack as the sync input; White Lightning uses ¼ in stereo jacks; Pocket Wizard (radio trigger) and Alien Bees use 3.5 mm mono jacks.

★ Some cameras (for example, Canon, Sigma, and Pentax DSLRs) use the 2.5mm stereo jack for the connector for the remote shutter release (and focus activation); examples are Canon's RS-60E3 remote switch and Sigma's CR-21 wired remote control.

★ Some miniaturized electronic devices use 2.5 or 3.5 mm jack plugs as serial port connectors for data transfer and unit programming. This technique is particularly common on graphing calculators and some types of amateur and two-way radio, though in some more modern equipment USB mini-B connectors are provided in addition to or instead of jack connectors.

Misuse

Jack connectors should 'not' be used as power connectors, since the contacts will often short together when a jack is inserted or removed. Some older effects units built by Alesis (such as the microVerb) did use a 3.5 mm two-conductor jack to connect AC power to the unit from a 9-Volt external transformer, but when this jack was removed or replaced while the PSU was powered up, the resulting momentary short-circuit would often destroy the unit's power supply.

Switch contacts

Panel-mounting jacks are often provided with switch contacts. Most commonly, a mono jack is provided with a single normally closed (NC) contact, which is connected to the tip (live) connection when no plug is in the socket, and disconnected when a plug is inserted. Stereo sockets commonly provide two such NC contacts, one for the tip (left channel live) and one for the ring or collar (right channel live). Some designs of jack also have such a connection on the sleeve, as this contact is usually ground it is not much use for signal switching but could be used to indicate to electronic circuitry that the socket was in use.
Less commonly, some jacks are provided with normally open (NO) or change-over contacts, and/or the switch contacts may be isolated from the connector.
The original purpose of these contacts was for switching in telephone exchanges, for which there were many patterns. Two sets of change-over contacts, isolated from the connector contacts, were common. The more recent pattern of one NC contact for each signal path, internally attached to the connector contact, stems from their use as headphone jacks. In many amplifiers and equipment containing them, such as electronic organs, a headphone jack is provided that disconnects the loudspeakers when in use. This is done by means of these switch contacts. In other equipment, a dummy load is provided when the headphones are not connected. This is also easily provided by means of these NC contacts.
Other uses for these contacts have been found. One is to interrupt a signal path to enable other circuitry to be inserted. This is done by using one NC contact of a stereo jack to connect the tip and ring together when no plug is inserted. The tip is then made the output, and the ring the input (or vice versa), thus forming a patch point.
Another use is to provide alternative mono or stereo output facilities on some guitars and electronic organs. This is achieved by using two mono jacks, one for left channel and one for right, and wiring the NC contact on the right channel jack to connect the two connector tips together when the right channel output is not in use. This then mixes the signals so that the left channel jack doubles as a mono output.
Where a 3.5 mm or 2.5 mm jack is used as a DC power inlet connector, a switch contact may be used to disconnect an internal battery whenever an external power supply is connected, to prevent incorrect recharging of the battery.
A three-conductor signal input socket is used on some battery-powered guitar effects pedals to eliminate the need for a separate power switch. When the user plugs in a two-conductor guitar or microphone lead, the resulting short-circuit between earth and ring connects an internal battery to the unit's circuitry, ensuring that it powers up or down automatically whenever a signal lead is inserted or removed. A side effect is the risk of inadvertently discharging the battery if the lead is not removed after use, for example if equipment is left connected overnight.

Tip/ring/sleeve terminology

In twisted pair wiring to this day, the non-inverting and/or "live" wire of each pair is known as the 'ring', while the inverting and/or "earthy" wire is known as the 'tip', inherited from the traditional connection via the TRS connector in telephone systems. If the pair is shielded, or if the pair is accompanied by a dedicated earth wire, this third conductor is known as the 'sleeve'. This usage corresponds to the connection to a three-connector jack plug in a manual telephone exchange. This appears to have originated with the use of 'TRS' jacks by switchboard operators with the tip and ring wires attached to the corresponding parts of the jack. Originally, the ''hot'' and ''ground'' were reversed, but often the metallic desktops of the switch boards were scarred by the discharge from the tips and the system was reversed to the present usage.
The term 'tip ring sleeve' is more common in some English-speaking countries than others. Outside of the USA the term ''stereo jack plug'' is probably more common, even for connectors not used for stereo. The modern profile three-conductor jack plug was originally designed for stereo signal connections, with left channel on the tip, right on the ring and common return on the body or sleeve. The term 'TRS' is particularly appropriate to distinguish these three-conductor (stereo) plugs used in other than stereo applications.

	Unbalanced Output	Unbalanced Input	Unbalanced Insert	Balanced	Stereo
Tip	Signal	Signal	Send or Return signal	Positive/"Hot"	Left channel
Ring	Ground or ''No Connection''	Ground or ''No Connection''	Return or Send signal	Negative/"Cold"	Right channel
Sleeve	Ground	Ground	Ground	Ground	Ground

:Note that early QSC amplifiers used a Tip Negative, Ring Positive input jack wiring scheme. ^[4]
::Whirlwind Line Balancer/Splitters do not use the Sleeve as a conductor on their unbalanced ¼ in TRS input. Tip and Ring are wired to the transformer's two terminals; Sleeve is not connected. ^[5]

Usage

Audio

When a TRS is used to make a balanced connection, the two active conductors are both used for a monaural signal. The ring, used for the right channel in stereo systems, is used instead for the inverting input. This is a common use in small audio mixing desks, where space is a premium and they offer a more compact alternative to XLR connectors. Another advantage offered by TRS connectors used for balanced microphone inputs is that a standard unbalanced signal lead using a mono jack plug can simply be plugged into such as input. The ring (right channel) contact then makes contact with the plug body, correctly grounding the inverting input.
The disadvantage of using TRS jacks for balanced audio connections is that the ground mates last and the socket grounds the plug tip and ring when inserting or pulling out the plug. This causes bursts of hum, cracks and pops and may stress some outputs as they will be short circuited briefly, or longer if the plug is left half in. Professional audio equipment uses XLR connectors which mate the ground signal on pin 1 first.
TRS connectors are also commonly used as unbalanced audio 'patch points' (or 'insert points', or simply 'inserts'), with the output on many mixers found on the tip (left channel) and the input on the ring (right channel). This is often expressed as "tip send, ring return." Other mixers have unbalanced insert points with "ring send, tip return." One advantage of this system is that the switch contact in the panel socket, originally designed for other purposes, can be used to close the circuit when the patch point is not in use. Another is that if the "tip send" patch point is used as an output only, use of a mono jack plug correctly grounds the input. In the same fashion, use of a "tip return" insert style allows a mono jack plug to bring an unbalanced signal directly into the circuit, correctly grounding the output. Combining Send and Return functions via single 6.35 mm TRS connectors in this way is seen in very many professional and semi-professional audio mixing desks, due to the halving of space needed for insert jack fields which would otherwise require two jacks, one for Send and one for Return. The tradeoff is that unbalanced signals are more prone to buzz, hum and outside interference.
In some TRS inserts, the concept is extended by using specially designed TRS jacks that will accept a mono jack plug partly inserted ("to the first click") and will then connect the tip to the signal path without breaking it. Most standard TRS jacks can also be used in this way with varying success, but neither the switch contact nor the tip contact can be relied upon unless the internal contacts have been designed with extra strength for holding the plug tip in place. Even with stronger contacts, an accidental mechanical movement of the inserted plug can interrupt signal within the circuit. For maximum reliability, any usage involving "first click" or "half-click" will instead rewire the plug to short Tip and Ring together and then insert this modified plug all the way into the jack.
The TRS Tip Return, Ring Send unbalanced insert configuration is mostly found on older mixers. This allowed for the insert jack to serve as a standard-wired mono line input that would bypass the mic preamp (and likely a resistive pad, as well as other circuitry, depending on the design), and thus improve sound quality. However tip send has become the generally accepted standard for mixer inserts since the early-to-mid 1990s. The TRS Ring Send configuration is still found on some compressor sidechain input jacks such as dbx 166XL.
In some very compact equipment, 3.5 mm TRS jacks are used as patch points.
Some sound recording devices use a TRS as a mono microphone input, using the tip as the signal path and the ring to connect a standby switch on the microphone.

Computer sound

Personal computer sound cards from Creative Labs, Sound Blaster or compatible to these use a 3.5 mm TRS as a mono microphone input, and deliver a 5 V polarising voltage on the ring to power electret microphones from the card manufacturer. Sometimes called ''phantom power'', this is not a suitable power source for microphones designed for true phantom power and is better called ''bias voltage''. Compatibility between different manufacturers is unreliable.
Normally, 3.5 mm 3-conductor sockets are used in computer soundcards for stereo output. Thus, for a soundcard with 5.1 output, there will be 3 sockets to accommodate 6 channels - front left & right, rear left & right, and center & subwoofer. But the 6.1 and 7.1 channel soundcards from Creative Labs are equipped with 1 and 2 sockets of 3.5 mm 4-conductor sockets respectively. This is to accommodate rear-center (6.1) or side left & right (7.1) channels without additional sockets on the sound card. But speaker have normal 3-conductor sockets. In Creative's documentation, the word "pole" is used instead of "conductor".
The Apple PlainTalk microphone jack used on some older Macintosh systems is designed to accept an extended 3.5 mm TRS; in this case, the tip carries power for a preamplifier inside the microphone. If a PlainTalk-compatible microphone is not available, the jack can accept a line-level sound input, though it cannot accept a standard microphone without a preamp.
Nowadays, all of Apple's computers have combination electric/optical 3.5 mm TRS jacks for both input and output. This allows for conventional stereo input and output with electrical connections, or 5.1 digital input and output with a mini-Toslink cable.
'Plug-in power'
( from: http://www.epanorama.net/circuits/microphone_powering.html )

Recording equipment

Many small video cameras, laptops, Minidisc recorders and other consumer devices use a 3.5 mm microphone connector for attaching a (mono/stereo) microphone to the system.
These fall into three categories:

★ Devices (usually of the "toy" variety), which use an un-powered microphone: usually a cheap dynamic or piezo microphone. The microphone generates its own voltage, and does not require power.

★ Devices (usually very expensive recorders, for hi-fi or broadcast use) which use a self-powered microphone: usually an expensive dynamic microphone with internal battery-powered amplifier.

★ Devices (most consumer equipment) which use a "plug-in powered" microphone: an electret microphone containing an internal FET amplifier. These provide a good quality signal, in a very small microphone. However, the internal FET requires a DC power supply, which is provided as a bias voltage.
Plug-in power is supplied on the same line as the audio signal, using an RC filter. The DC bias voltage supplies the FET amplifier (at a low current), while the capacitor decouples the DC supply from the AC input to the recorder. Typically, V=1.5 V, R=1 kΩ, C=47 µF.
If a recorder provides plug-in power, and the microphone does not need it, everything will usually work ok, although the sound quality may be lower than expected. In the converse case (recorder provides no power; microphone requires power), no sound will be recorded. Neither misconfiguration will damage
consumer hardware, but it could destroy a broadcast-type microphone.

Aircraft headsets

Commercial and general aviation civil airplane headset plugs are similar, but with a difference. A standard 1/4-inch monaural plug, type PJ-055, is used for headphones, paired with special tip-ring-sleeve, 0.206 inch diameter plug, type PJ-068, for the microphone. The extra connection in the microphone plug is used by an optional push-to-talk switch.
Military aircraft and civil helicopters have another type similar to a standard 1/4-inch stereo plug, but with a 0.281-inch diameter short shaft with an extra sleeve, known by the designation U-174/U. This provides four connections in one plug, allowing for a pair of monaural headphones, a microphone, a push-to-talk switch and a common ground conductor.
Some mobile phones such as the Nokia N95 and the Apple iPhone also use a similarly-wired plug for their headphone/microphone set.

Configurations and schematic symbols

These examples are meant to illustrate each possible component of such jacks, but many other configurations using these basic components are available. All examples in the above figure are oriented so the plug 'enters' from the right.
'A.' A simple two-conductor jack. The connection to the sleeve is the rectangle towards the right, and the connection to the tip is the line with the notch. Wiring connections are illustrated as white circles.
'B.' A three-conductor, or TRS, jack. The upper connector is the tip, as it is farther away from the sleeve. The sleeve is shown connected directly to the chassis, a very common configuration. This is the typical configuration for a balanced connection. Some jacks have metal mounting connections (which would make this connection) and some have plastic, to isolate the sleeve from the chassis, and provide a separate sleeve connection point, as in 'A'.
'C.' This three-conductor jack has two isolated SPDT switches. They are activated by a plug going into the jack, which disconnects one throw and connects the other. The white arrowheads indicate a mechanical connection, while the black arrowheads indicate an electrical connection. This would be useful for a device that turns on when a plug is inserted, and off otherwise, with the power routed through the switches.
'D.' This three-conductor jack has two normally closed switches connected to the contacts themselves. This would be useful for a patch point, for instance, or for allowing another signal to feed the line until a plug is inserted. The switches open when a plug is inserted. A common use for this style of connector is a stereo headphone jack that shuts off the default output (speakers) when the connector is plugged in.

See also

★ RCA connector

★ XLR connector

References

1. International Library of Technology: ...Principles of Telephony..., , , , International Textbook Company, Scranton, PA, 1907,
2. Radio Production, Robert McLeish, , , Newnes, 2005,
3. The Sound Reinforcement Handbook, Gary D. Davis and Ralph Jones, , , Hal Leonard, 1989,
4. http://www.qscaudio.com/support/technical_support/faq.htm#pafaq6
5. http://www.whirlwindusa.com/ftp/Blackbox/manuals/lbs.pdf